Adjustable three electrode spark gap



May l5, 1970 w. A. CARTER vAL'USTBILJB. THREE ELECTRODE SPARK GAP FiledNOV. 17. 1967 vBY United States Patent U.S. Cl. 313-147 5 ClaimsABSTRACT F THE DISCLOSURE A spark gap switch is provided with threeadjustable electrodes making it useful over a Wide range of voltages andmaking it possible to readjust the gap Spacings between the triggerelectrode and the main electrodes and between the main electrodesthemselves. The trigger electrode is further provided with a sealedsource of radioactive material which stabilizes the flashover voltagevalue and insures consistency by nullifying the effect of any randomionization in the gaps. The electrodes are further arranged to producemagnetic movement of the arc away from critical surfaces. The spark gapswitch is also provided with terminals at opposite ends of the switch tomake high voltage connection possible from either end.

Background of the invention This invention relates to spark gapswitches, and more particularly relates to spark gap switches which canbe adjusted with great ease and precision.

Precision spark gap switches have numerous uses. For example, high speedcircuit breakers have been developed using discharge capacitors whichdischarge into various types of coils to produce very rapid physicalresponse of the circuit breaker tripping mechanism. To accomplish this,it is required that a charged capacitor be connected to a coil by anextremely fast switch such as a spark gap having high current capacityto accommodate the high discharge current of the capacitor which canoften exceed 10,000 amperes peak. The gap must also withstand thecapacitor voltage which could be from 1.5 kv. to kv. The spark gapswitch must respond rapidly and reliably to protect the capacitor.

A spark gap can fulfill the needs of a high capacity, high speed(essentially zero time) switch for use in such circuit breakers, butsuch gap, to be practical, must have suHicient adjustability to beusable over a wide range of voltages. Such spark gap switches have notheretofore been commercially available.

Spark gap switches have previously been used in high voltagetransmission lines to protect series capacitors in the lines byby-passing such capacitors when the voltages are above an acceptablelevel.

While this application of spark gaps to cause instantaneous by-passingof capacitors when the voltage eX- ceeds a predetermined value, andthereby discharging the capacitors across the spark gap circuit, isknown, serious problems exist in adapting these spark gap switches foruse in high speed circuit breakers.

A serious problem existing in the field of spark gap switches is thatthe spark gap devices in the past have been manufactured with specificvoltage requirements so that they cannot be used economically insituations where the voltage requirements change. In addition, thesespark gap devices have limited useful lives since the arcs between theelectrodes of these devices cause erosion of the electrodes and therebychange the spark-over characteristics of the spark gap. The change inspark-over char- ICC acteristics of the particular device makes itunsuitable for the particular situation for which it was designed.

Several methods have been used in the past to attempt to solve theseproblems, but they have had only limited success. One method used in thepast has been the use of an adjustable precision spark gap as shown inU.S. Pat. No. 3,229,145 to O. Jensen and assigned to the assignee of theinstant invention. This device, however is a two terminal spark gap andis, therefore, not designed to be triggered. Furthermore, in this devicethe terminal electrodes are situated at opposite ends of the device andthese electrodes have limited accessibility since they are frequentlysituated so that one may be inaccessible.

Another method shown 'in U.S. Pat. No. 3,259,792 to O. Jensen andassigned to the assignee of the instant invention employs a threeterminal spark gap device in which the two outer terminals areadjustable. In this device, however, it is merely the outside electrodeswhich are controllable and there is no independent control of thetriggering electrode.

The instant invention solves the problems previously existing byproviding a spark gap device with a novel arrangement of threeadjustable electrodes.

In one embodiment of the invention a novel spark gap switch is providedwith three adjustable electrodes. The two outer electrodes are providedwith special arc resistant conductive material such as Elkonite, atrademark of P. R. Mallory & Co., tungsten or the like. The separationbetween these two electrodes constitutes the main spark gap. The twoelectrodes are adjustable so that the spark gap may be shortened orenlarged to provide for changed voltage requirements or for changesnecessitated by any flashover characteristic changes due to electrodeerosion. The novel spark gap device is provided with an adjustable thirdelectrode. This electrode constitutes the trigger electrode and isadjustable independently of the other two electrodes. The triggerelectrode is also provided with a sealed source of radioactive material,such as radioactive Cobalt-60, to establish a basic ionization levelwithin the spark gap which is significantly greater than the strayionization in the gap and thereby stabilizes the flashover value andinsures consistency.

It is one object of the instant invention to provide a novel spark gapswitch usable over a wide range of voltages.

It is another object of this invention to provide a spark gap switchcapable of carrying high currents.

It is a further object of this invention to provide a spark gap switchusable in a high speed circuit breaker employing discharge capacitors.

Another object of this invention is to provide a spark gap switch havingthree adjustable electrodes so that the flashover voltage between themain electrodes and the ilashover voltage between the trigger electrodeand a main electrode may be adjusted independently.

Another object of this invention is to provide a spark gap switch whichmay be adjusted to produce desired ashover characteristics even-afterthere has been electrode erosion due to long use.

A further object of this invention is to provide a spark gap switch withelectrodes having arc resistant tips to insure their long life.

Another object of this invention is to provide a spark gap switch withmeans to produce magnetic movement of the arc away from criticalsurfaces thus prolonging the useful life of the device by preventingelectrode erosion.

Another object of the instant invention is to provide a spark gap deviceincluding a triggering electrode which improves the consistency of thespark-over voltage of the gap by establishing a basic ionization levelWithin 3 the gap which is significantly greater than stray ionizationwhich may occur within the gap.

It is another object of this invention to provide a novel precisionspark gap switch having electrodes which are accessible at either of twoends for high voltage connection.

It is a further object of this invention to provide a spark gap switchwhich is economical in that it has a long life and it is simple andinexpensive to manufacture.

These and other objects of this invention will become apparent from thefollowing description when taken in connection with the drawing.

FIG. 1 shows a side cross-sectional view of a spark gap constructed inaccordance with the present invention; and

FIG. 2 shows a cross-sectional view of the spark gap switch taken alongline 2-2 of FIG. 1.

Referring to the drawings, there is shown the novel spark gap of theinvention as comprised of a cylindrical housing 11 of Lucite or othersuitable transparent material. One end of housing 11 is supported byepoxy top plate 12 which is designed with mounting holes (not shown) sothat it may `be secured to a suitable surface. The other end of housing11 is supported by bottom plate 13.

The main electrode terminals 14 and 15 are formed of high activity boltswhich are supported by top plate 12 and bottom plate 13 and secure theplates 12 and 13 to housing 11. Terminals 14 and 15 are accessible fromeither the top or ybottom of the device, thus making circuit connectioneasier even if the top or bottom of the device is covered orinaccessible when the device is mounted. The electrode terminals 14 and15 are threaded at both ends to permit their secure mounting to plate 12by nuts 16 and 17, respectively, and to plate 13 by nuts 18 and 19. Theelectrode terminals 14 and 15 slidably t into holes in plates 12 and 13so that they may be moved when the nuts at their respective ends are notin engagement with the surfaces of plates 12 and 13. The electrodeterminals 14 and 15 also each include an enlarged central body 21 and22, respectively.

Electrode arms 23 and 24 are formed of bent beryllium copper prestressedstraps provided with suitable mounting holes and are secured toelectrode terminals 14 and 15, respectively, yby means of nuts 25 and26, respectively. The lower ends of electrode arms 23 and 24 areprovided with arc resistant tips 27 and 28, respectively, which may beElkonite or other suitable material.

The spark gap switch includes a third electrode 30. The electrode 30 isthe trigger electrode of the spark gap switch. This electrode includes asealed compartment for housing radioactive material 31. The radioactivematerial 31 may be Cobalt-60. The trigger electrode 30 also includes atip 32 which may also be made of arc resistant material such asElkonite. The trigger arm 30 includes a threaded portion 33 and a head34 which may be of a hexagonal shape.

The trigger electrode 30 adjustably fits into cylindrical member 35 bymeans of its threaded portion 33 and the nut 36 attached to the end ofmember 35. At the opposite end of member 35 is a cylindrical taperedportion 37. This tapered portion 37 may be made of nylon or othersuitable material. The cylindrical tapered portion 37 includes athreaded hole through which the threaded portion 33 of trigger electrode30 passes. The member 35 also includes a pair of threaded portions 38separated by a pair of flat surfaces (not shown). Threaded portions 38engage the threaded portion of a hole in top plate 12 and nut 40 tosecure the member 35 and its cylindrical tapered portion 37 in place.The fiat surfaces are engageable by a wrench or the like for adjustingthe position of member 35 and its tapered portion 4 37. The member 35and its tapered portion 37 are made of suitable insulation material.

In the novel spark gap switch described all three electrodes areadjustable to control the breakdown voltage necessary to producetiashover in the spark gap. By means of the adjustment of member 35 bythe screw action of its thread 38 and the thread in top plate 12 and nut40, the tapered cylindrical portion 37 may be moved. The movement oftapered portion 37 adjusts the distance between the main electrodes 27and 28 by means of the creepage of straps 23 and 24 along the taperedmember 37 Trigger electrode 30 may also be adjusted by means of thescrew action of its thread 33 and the nut 36 and the threaded hole ofmember 35.

It is, therefore, seen that the breakdown voltage between the triggerelectrode 30 and the electrode arms 23 and 24 may be independentlyadjusted and the breakdown voltage between the electrode arms 23 and 24may be independently adjusted.

When there is a flashover in the gap between the electrode arms 23 and24 a concentrated magnetic field is established in the region betweenthe electrode arms as a result of the current flowing through theseelectrode arms. The magnetic eld in the region causes the magneticmovement of the arc between electrode tips 27 and 28 away from thecritical surfaces by means of the blowout effect. This magnetic field isestablished as a result of the U-shaped relationship of the contact arms23 and 24.

The spark gap switch operates so that under a predetermined voltagecondition, the voltage between the trigger electrode 30 and one of themain terminals 14 or 15 is suiicient to cause a fiashover between tip 32and tip 27 or 28. The liashover ionizes the gases in the spark gapbetween tips 27 and 28 and, hence, permits a flashover between these twotips to short any circuit connected across the terminal electrodes 14and 15.

The instant invention provides a novel spark gap switch which is easy tomanufacture and assemble and has a wide range of voltages over which itis usable. For instance, the instant invention may be made adjustableover a voltage range from 1.5 kv. to approximately 15 kilovolts.

Although the instant invention has been described with respect to apreferred embodiment thereof, it should be understood that manyvariations and modifications will now be obvious to those skilled in theart, and it is preferred, therefore, that the scope of this inventionnot be limited by the specific disclosure herein, but only by theappended claims.

The embodiments of the invention in which an exclusive privilege orproperty is claimed are defined as follows:

1. A spark gap switch comprising:

a main support body;

iirst and second arcing electrodes connected to said main support bodyand held in spaced relation to one another; a third electrode disposedadjacent to and spaced from at least one of said first and second arcingelectrodes;

adjustable support means connecting said third arcing electrode to saidmain support body; said adjustable support means comprising a cylinderextending through said main support body and a central shaft extendingthrough said cylinder; said cylinder being longitudinally movable withrespect to said main support body; one end of said cylinder connected toat least one of said iirst or second arcing electrodes and moving saidat least one of said first and second arcing electrodes with respect tothe other responsive to longitudinal movement of said cylinder;

said third electrode connected to the end of said shaft adjacent saidone end of said cylinder and being longitudinally movable with respectto said cylinder, thereby to alter the position of said third electrodewith respect to said at least one of said first and second arcingelectrodes.

2. A spark gap switch as defined in claim 1 wherein said main supportbody includes first and second end plates and first and second bolts,each of said bolts being accessible on the exterior side of either ofsaid end plates; said first and second bolts being connected to saidfirst and second arcing electrodes, respectively.

3. A spark gap switch as defined in claim 1 wherein said first andsecond arcing electrodes define a U-shaped current path thereby settingup an electromagnetic field which causes magnetic movement of any arcaway from aninitial arcing position.

4. A spark gap switch as defined in claim 3 wherein the end of saidcylinder of said adjustable support means which is connected to at leastone of said first or second arcing electrodes is tapered and whereineach of said first and second arcing electrodes includes a conductingstrap which is biased against said tapered end of said cylinder so thatlongitudinal movement of said cylinder causes movement of said first andsecond arcing electrodes with respect to each other.

S. A spark gap switch comprising:

a main support body;

first and second arcing electrodes connected to said main support bodyand held in spaced relation to one another;

said first and second arcing electrodes each including a conductingstrap positioned so that said first and second electrodes define aU-shaped current path;

adjustable support means comprising a cylinder extending through saidmain support body and being longitudinally movable with respect to saidmain support body;

said cylinder having a tapered end which is connected to at least one ofsaid conducting straps of said first or second arcing electrode andmoving said at least one of said first or second arcing electrode withrespect to the other responsive to longitudinal movement of saidcylinder.

References Cited UNITED STATES PATENTS 2,472,115 `6/1949 Mayer 313-147 XJAMES W. LAWRENCE, Primary Examiner R. F. HOSSFELD, Assistant ExaminerU.S. Cl. X.R.

